1. Technical Field
The present invention relates to methods of manufacturing III-nitride crystals and III-nitride crystal substrates having a major surface whose variance in crystallographic plane orientation, with respect to an {hkil} plane that is a crystallographic plane chosen exclusive of the {0001} form, is slight (h, k, i and l herein being whole numbers, with the relationship i=−(h+k) holding—likewise hereinafter). The present invention also relates to methods of manufacturing semiconductor devices including such III nitride crystal substrates.
2. Description of the Related Art
Group-III nitride crystals, which are employed advantageously in light-emitting devices, electronic devices and semiconductor sensors, are ordinarily manufactured by growing crystal onto the major surface of a sapphire substrate having a (0001)-plane major surface, or onto a GaAs substrate having a (111) a-plane major surface, by means of a vapor-phase technique such as hydride vapor-phase epitaxy (HVPE) or metalorganic chemical vapor deposition (MOCVD), or by flux growth or other liquid-phase technique. Consequently, ordinarily obtained III-nitride crystals have a major surface whose crystallographic plane orientation is {0001}.
With light-emitting devices on substrates that are III-nitride crystal having a major surface whose crystallographic plane orientation is {0001}, and in which a multiquantum-well (MQW) structure as a light-emitting layer has been deposited on the major surface, the light-emission efficiency is compromised by spontaneous polarization that occurs within the light-emitting layer owing to the III-nitride crystal's <0001> oriented polarity. Consequently, the manufacture of III-nitride crystal having a major surface whose plane crystallographic orientation is other than {0001} is being sought.
The following several methods have been proposed as ways of creating gallium-nitride crystal having a surface plane orientation of choice, without influencing the crystallographic plane orientation of the major surface of the substrate.
Japanese Unexamined Pat. App. Pub. No. 2005-162526 (Patent Document 1) for example discloses a method in which a number of rectangular crystal boules are sliced from GaN crystal grown by vapor deposition, and meanwhile, a silicon oxide film is coated onto the surface of a separately readied sapphire substrate, and then a number of recesses reaching to the substrate are formed in the film, the numerous crystal boules are embedded into the recesses in a manner such that their top surfaces will have the same desired plane orientation of choice, and by vapor deposition with the crystal boules as seeds, gallium nitride crystal having a surface plane orientation of choice is grown.
Furthermore, Japanese Unexamined Pat. App. Pub. No. 2006-315947 (Patent Document 2) discloses a method in which a number of nitride semiconductor bars are arranged in such a way that the c faces of adjoining nitride semiconductor bars oppose each other and the m face of each nitride semiconductor bar is the upper face, and nitride semiconductor layers are formed onto the upper face of the thus arranged nitride semiconductor bars.    Patent Document 1: Japanese Unexamined Pat. App. Pub. No. 2005-162526    Patent Document 2: Japanese Unexamined Pat. App. Pub. No. 2006-315947
With the method in the just-noted Patent Document 1, however, inasmuch as growth of the GaN crystal is carried out with, as seeds, the boules of crystal GaN that have been embedded into the sapphire substrate, due to the disparity in thermal expansion coefficient between sapphire and GaN, fractures and strain occur in the GaN crystal when the crystal is cooled following the growth process, such that GaN crystal of superior crystallinity has not been obtainable.
Furthermore, if III-nitride crystal containing Al—for example, AlxGayIn1−x−yN (x>0, y≧0, x+y≦1)—is grown by the method in above-noted Patent Document 1, because the Al precursor is not selective with respect to the silicon oxide film, the AlxGayIn1−x−yN grows onto the silicon oxide film as well, and consequently AlxGayIn1−x−yN crystal of superior crystallinity has not been obtainable.
With the method in just-noted Patent Document 2, meanwhile, inasmuch as the c-planes of the nitride semiconductor bars are set in opposition, nitride semiconductor layers having a chosen crystallographic plane orientation other than planes (such as the m-plane, for example) perpendicular to the c-plane have not been obtainable.
Moreover, the nitride semiconductor bars used in the method of above-noted Patent Document 2 are rectangular striplike slices of a nitride semiconductor wafer grown onto a dissimilar wafer, such as sapphire, SiC, silicon or GaAs, having a chemical composition that is of a different kind from that of the nitride semiconductor. In this case, the nitride semiconductor wafer grown onto the dissimilar wafer possesses significant crystal strain and warp, on account of which the variance in crystallographic plane orientation, with respect to the m-plane, across the major surface of nitride semiconductor bars sliced from such a nitride semiconductor wafer is considerable. For that reason, nitride semiconductor layers grown onto the m-plane of the plurality of nitride semiconductor bars also prove to have considerable variance in crystallographic plane orientation across the major surface with respect to the m-plane. Such inconsistency compromises the device properties of semiconductor devices that incorporate such nitride semiconductor layers, and is deleterious to production yields.